Apparatus and method for transmitting channel quality indicator and acknowledgement signals in SC-FDMA communication systems

ABSTRACT

A method and apparatus for transmitting information symbols in a communication system are provided. The method includes determining a Channel Quality Indicator (CQI) and acknowledgement information, in response to data reception; generating a first symbol based on the CQI and a second symbol based on the acknowledgement information; and transmitting the first symbol and the second symbol. A first code is applied to the second symbol, when the acknowledgement information is negative, a second code is applied to the second symbol, when the acknowledgement information is positive, and the first code is applied to the second symbol, when the acknowledgement information does not exist.

PRIORITY

This application is a Continuation of U.S. application Ser. No.12/174,098, which was filed in the U.S. Patent and Trademark Office(USPTO) on Jul. 16, 2008, and claims priority under 35 U.S.C. §119 toU.S. Provisional Application No. 60/950,002, which was filed in theUSPTO on Jul. 16, 2007, to U.S. Provisional Application No. 60/954,171,which was filed in the USPTO on Aug. 6, 2007, and to U.S. ProvisionalApplication No. 61/019,624, which was filed in the USPTO on Jan. 8,2008, the content of each of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed, in general, to wireless communicationsystems and, more specifically, to a Single-Carrier Frequency DivisionMultiple Access (SC-FDMA) communication system and is further consideredin the development of the 3^(rd) Generation Partnership Project (3GPP)Evolved Universal Terrestrial Radio Access (E-UTRA) Long Term Evolution(LTE).

2. Description of the Art

In particular, the present invention is directed to the transmission ofpositive or negative acknowledgement signals (ACKs or NACKs,respectively) and Channel Quality Indicator (CQI) signals over the sametransmission time interval in an SC-FDMA communication system.

Several types of signals should be supported for the properfunctionality of the communication system. In addition to data signals,which convey the information content of the communication, controlsignals also need to be transmitted from User Equipments (UEs) to theirserving Base Station (BS or Node B) in the UpLink (UL) of thecommunication system and from the serving Node B to the UEs in theDownLink (DL) of the communication system in order to enable the propertransmission of data signals.

The present invention considers the UL communication and assumes thatthe transmission of signals carrying the data content information fromUEs is through a Physical Uplink Shared CHannel (PUSCH) while, in theabsence of data information, the transmission of control signals fromthe UEs is through the Physical Uplink Control CHannel (PUCCH). A UE,also commonly referred to as a terminal or a mobile station, may befixed or mobile and may be a wireless device, a cellular phone, apersonal computer device, a wireless modem card, etc. A Node B isgenerally a fixed station and may also be called a Base TransceiverSystem (BTS), an access point, or some other terminology.

The ACK/NACK is a control signal associated with the application ofHybrid Automatic Repeat reQuest (HARQ) and is in response to the corrector incorrect, respectively, data packet reception in the DL of thecommunication system (also known as HARQ-ACK). A data packet isretransmitted after the reception of a NACK and a new data packet may betransmitted after the reception of an ACK.

The CQI is another control signal that provides information to theserving Node B about the channel conditions, such as theSignal-to-Interference and Noise Ratio (SINR), experienced in portionsof or over the entire DL operating bandwidth. The present inventionfurther considers that the ACK/NACK and CQI transmissions are in theabsence of any data transmission from a reference UE.

The UEs are assumed to transmit data or control signals over aTransmission Time Interval (TTI), which in an exemplary embodiment ofthe present invention corresponds to a sub-frame.

FIG. 1 illustrates a block diagram of a sub-frame structure 110 assumedin an exemplary embodiment of the present invention. The sub-frameincludes two slots. A first slot 120 further includes seven symbols usedfor the transmission of data and/or control signals. Each symbol 130further includes a Cyclic Prefix (CP) in order to mitigate interferencedue to channel propagation effects. The signal transmission in one slotmay be in the same part or it may be at a different part of theoperating bandwidth than the signal transmission in the other slot. Inaddition to symbols carrying data or control information, some symbolsmay be used for the transmission of Reference Signals (RS), also knownas pilots, used to provide channel estimation and enable coherentdemodulation of the received signal. It is also possible for the TTI toinclude only one slot or more than one sub-frames.

The transmission BandWidth (BW) is assumed to include frequency resourceunits that will be referred to herein as Resource Blocks (RBs). Anexemplary embodiment of the present invention assumes that each RBincludes 12 sub-carriers, and that UEs are allocated a multiple N ofconsecutive RBs 140 for PUSCH transmission and 1 RB for PUCCHtransmission. Nevertheless, it should be noted that the above values areonly illustrative and should be not restrictive to the describedembodiments of the invention.

FIG. 2 illustrates an exemplary structure for a CQI transmission duringone slot 210 in a SC-FDMA communication system. The CQI information bits220, through modulators 230, modulate a Constant Amplitude ZeroAuto-Correlation (CAZAC) sequence 240, for example with QPSK or 16QAMmodulation, which is then transmitted by the UE, after performing anInverse Fast Fourier Transform (IFFT) operation as it is furthersubsequently described. In addition to the CQI, RS is transmitted toenable coherent demodulation at the Node B receiver of the CQI signal.In an exemplary embodiment, the second and sixth SC-FDMA symbols in eachslot carry the RS transmission 250.

As mentioned above, the CQI and RS signals are assumed to be constructedfrom CAZAC sequences. An example of such sequences is given by thefollowing Equation (1):

$\begin{matrix}{{c_{k}(n)} = {{\exp\left\lbrack {\frac{{j2\pi}\; k}{L}\left( {n + {n\frac{n + 1}{2}}} \right)} \right\rbrack}.}} & (1)\end{matrix}$

In Equation (1), L is a length of the CAZAC sequence, n is an index ofan element of the sequence n={0, 1, 2 . . . , L−1}, and k is an index ofthe sequence itself For a given length L, there are L−1 distinctsequences, if L is prime. Therefore, an entire family of sequences isdefined as k ranges in {1, 2 . . . , L−1}. However, it should be notedthat the CAZAC sequences used for the CQI and RS generation need not begenerated using the exact above expression as will be further discussedbelow.

For CAZAC sequences of prime length L, the number of sequences is L−1.As the RBs are assumed to include an even number of sub-carriers, with 1RB including 12 sub-carriers, the sequences used to transmit theACK/NACK and RS can be generated, in the frequency or time domain, byeither truncating a longer prime length (such as length 13) CAZACsequence or by extending a shorter prime length (such as length 11)CAZAC sequence by repeating its first element(s) at the end (cyclicextension), although the resulting sequences do not fulfill thedefinition of a CAZAC sequence. Alternatively, the CAZAC sequences canbe directly generated through a computer search for sequences satisfyingthe CAZAC properties.

An exemplary block diagram for a transmission of a CAZAC sequencethrough SC-FDMA signaling in the time domain is illustrated in FIG. 3.The structure illustrated in FIG. 3 can be used, for example, for theCQI transmission in the PUCCH.

Referring to FIG. 3, the CAZAC sequence 310 is generated through one ofthe previously described methods (modulated for transmission of CQIbits, un-modulated for RS transmission), and is then cyclically shifted320 as will be subsequently described. The Discrete Fourier Transform(DFT) of the resulting sequence is then obtained 330, the sub-carriers340 corresponding to the assigned transmission bandwidth are selected350, the IFFT is performed 360, and finally the cyclic prefix (CP) 370and filtering 380 are applied to the transmitted signal. Zero padding isassumed to be inserted by the reference UE in sub-carriers used for thesignal transmission by another UE and in guard sub-carriers (not shown).

Moreover, for brevity, additional transmitter circuitry such asdigital-to-analog converter, analog filters, amplifiers, and transmitterantennas as they are known in the art, are not illustrated in FIG. 3.Similarly, the encoding process and the modulation process for CQI bits,which are well known in the art, such as block coding and QPSKmodulation, are also omitted for brevity.

At the receiver, the inverse (complementary) transmitter functions areperformed. This is conceptually illustrated in FIG. 4, in which thereverse operations of those in FIG. 3 apply.

As it is known in the art (although not shown for brevity), an antennareceives the radio-frequency (RF) analog signal and after furtherprocessing units (such as filters, amplifiers, frequencydown-converters, and analog-to-digital converters) the digital receivedsignal 410 passes through a time windowing unit 420 and the CP isremoved 430. Subsequently, the receiver unit applies an FFT 440, selects450 the sub-carriers 460 used by the transmitter, applies an Inverse DFT(IDFT) 470, de-multiplexes (in time) the RS and CQI signal 480, andafter obtaining a channel estimate based on the RS (not shown), extractsthe CQI bits 490.

As for the transmitter, well known in the art receiver functionalitiessuch as channel estimation, demodulation, and decoding are not shown forbrevity and they are not material to the invention.

An alternative generation method for the transmitted CAZAC sequence isin the frequency domain, which is illustrated in FIG. 5.

Referring to FIG. 5, the generation of the transmitted CAZAC sequence inthe frequency domain follows the same steps as in the time domain withtwo exceptions. The frequency domain version of the CAZAC sequence isused 510 (that is, the DFT of the CAZAC sequence is pre-computed and notincluded in the transmission chain) and the cyclic shift 550 is appliedafter the IFFT 540. The selection 520 of the sub-carriers 530corresponding to the assigned transmission bandwidth, and theapplication of cyclic prefix (CP) 560 and filtering 570 to thetransmitted signal 580, as well as other conventional functionalities(not shown), are the same as previously described for FIG. 3.

The reverse functions are again performed for the reception of theCAZAC-based sequence transmitted as described in FIG. 5. As isillustrated in FIG. 6, the received signal 610 passes through a timewindowing unit 620 and the CP is removed 630. Subsequently, the cyclicshift is restored 640, an FFT 650 is applied, and the transmittedsub-carriers 660 are selected 665. FIG. 6 also illustrates thesubsequent correlation 670 with the replica 680 of the CAZAC-basedsequence. Finally, the output 690 is obtained, which can then be passedto a channel estimation unit, such as a time-frequency interpolator, incase of a RS, or can be used for detecting the transmitted information,in case the CAZAC-based sequence is modulated by the CQI informationbits.

As described above, if the transmitted CAZAC-based sequence illustratedin FIG. 3 or FIG. 5 is not be modulated by any information (data orcontrol), it can then serve as the RS. For CQI transmission, theCAZAC-based sequence is obviously modulated by the CQI information bits(for example, using QPSK modulation). FIG. 3 and FIG. 5 are thenmodified in a straightforward manner to include the real or complexmultiplication of the generated CAZAC sequence with the CQI informationsymbols. FIG. 2 illustrates such a modulation of a CAZAC sequence.

Different cyclic shifts of the same CAZAC sequence provide orthogonalCAZAC sequences. Therefore, different cyclic shifts of the same CAZACsequence can be allocated to different UEs in the same RB for their RSor CQI transmission, and achieve orthogonal UE multiplexing. Thisprinciple is illustrated in FIG. 7.

Referring to FIG. 7, in order for the multiple CAZAC sequences 710, 730,750, and 770 generated correspondingly from multiple cyclic shifts 720,740, 760, and 780 of the same root CAZAC sequence to be orthogonal, thecyclic shift value Δ790 should exceed the channel propagation delayspread D (including a time uncertainty error and filter spillovereffects). If T_(S) is the duration of one symbol, the number of cyclicshifts is equal to the mathematical floor of the ratio T_(S)/D. For 12cyclic shifts and for symbol duration of about 66 microseconds (14symbols in a 1 millisecond sub-frame), the time separation ofconsecutive cyclic shifts is about 5.5 microseconds. Alternatively, toprovide better protection against multipath propagation, only 6 cyclicshifts may be used providing time separation of about 11 microseconds.

The first exemplary setup of the present invention assumes that the ULslot structure for CQI transmission comprises of 5 CQI and 2 RS symbolsin 1 RB in each of the 2 slots of the sub-frame (the structure in oneslot is illustrated in FIG. 2, the same or a similar structure isrepeated for the second slot). During the first slot of the sub-framethe transmission is towards one end of the operating bandwidth andduring the second slot it is typically towards the other end of theoperating bandwidth (not necessarily the first or last RB of theoperating bandwidth, respectively). Nevertheless, transmission may beonly in one slot.

Occasionally, it is likely that a UE needs to transmit an ACK/NACKsignal, in response to a previously received data packet in the DL ofthe communication system during the same sub-frame the UE has its CQItransmission in the PUCCH (i.e., the UE has no information data totransmit in the PUSCH). To accomplish this transmission withoutaffecting the multiplexing capacity of ACK/NACK and CQI signals, theprior art considers that the UE suspends the CQI transmission in one ormore symbols in order to transmit the ACK/NACK information. This isillustrated in FIG. 8.

Comparing to an equivalent structure of FIG. 2 which does not have anyACK/NACK transmission in the slot 810, one SC-FDMA symbol used for CQItransmission is being replaced by an ACK/NACK transmission 820 leadingto a reduction in the number of CQI transmission symbols 830, 835 whilethe number of RS transmission symbols 840 remains unchanged. Similarlyto the CQI bits, the ACK/NACK bits modulate 850 a CAZAC-based sequence860. The same concept may apply on both slots of a sub-frame if thetransmission is over the sub-frame. Therefore, as is the case for theCQI and RS transmission, ACK/NACK is also transmitted by modulating aCAZAC sequence.

When multiplexing ACK/NACK transmission on the same slot or sub-frame asthe CQI transmission as illustrated in FIG. 8, a smaller number of CQIinformation bits should be transmitted in order to avoid decreasing thereliability of the CQI transmission. Alternatively, in order to transmitthe same number of CQI information bits a higher code rate should beused, thereby leading to reduced reliability for the received codewordand different coding and decoding processes (depending on whether or notACK/NACK is also transmitted).

In addition to degrading the CQI reception reliability or reducing theCQI transmission payload, the structure illustrated in FIG. 8 severelylimits the ACK/NACK performance as only one symbol per slot is used forACK/NACK instead of multiple symbols per slot as for example when onlyACK/NACK bits (no CQI bits) are transmitted in a slot (except in symbolshaving RS transmission, if any).

Therefore, puncturing CQI symbols to insert ACK/NACK symbols in thePUCCH is associated with significant performance disadvantages for thetransmission of both of these control signals.

Therefore, there is a need to multiplex ACK/NACK information bits in aCQI transmission sub-frame without penalizing the CQI or ACK/NACKperformance.

There is another need to multiplex transmission of ACK/NACK informationbits in a CQI transmission sub-frame without reducing the number of CQIinformation bits.

Finally, there is another need to multiplex transmission of ACK/NACKinformation bits in a CQI transmission sub-frame without substantiallychanging the transmitter or receiver structure relative to the case ofindividual transmission for either of these two control signals.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been designed to solve theaforementioned problems occurring in the prior art, and provide at leastthe advantages described below.

An aspect of the present invention is to provide an apparatus and methodfor multiplexing the transmission of acknowledgement (ACK/NACK) signalsand CQI signals from a User Equipment (UE).

Another aspect of the present invention is for the performance of CQItransmission with ACK/NACK multiplexing to be effectively the same asthe performance of CQI transmission without ACK/NACK multiplexing.

Another aspect of the present invention is to use the same number of CQIinformation bits with ACK/NACK multiplexing as without ACK/NACKmultiplexing.

Another aspect of the present invention is to use the ACK/NACKtransmission to achieve reliable performance.

Another aspect of the present invention is to use the multiplexing ofACK/NACK and CQI transmissions with substantially the same transmitterand receiver structures.

Another aspect of the present invention is to provide robust systemoperation for ACK/NACK and CQI multiplexing as the absence of ACK/NACKtransmission from a UE when its serving Node B expects such transmissioncauses only minor operational losses.

In accordance with an aspect of the present invention, a method isprovided for transmitting information symbols in a communication system.The method includes determining a Channel Quality Indicator (CQI) andacknowledgement information, in response to data reception; generating afirst symbol based on the CQI and a second symbol based on theacknowledgement information; and transmitting the first symbol and thesecond symbol. A first code is applied to the second symbol, when theacknowledgement information is negative, a second code is applied to thesecond symbol, when the acknowledgement information is positive, and thefirst code is applied to the second symbol, when the acknowledgementinformation does not exist.

In accordance with another aspect of the present invention, an apparatusis provided for transmitting information symbols in a communicationsystem. The apparatus includes a controller that determines a ChannelQuality Indicator (CQI) and acknowledgement information, in response todata reception; generates a first symbol based on the CQI and generatesa second symbol based on the acknowledgement information; and atransmitter that transmits the first symbol and the second symbol. Themultiplier applies a first code to the second symbol, when theacknowledgement information is negative, applies a second code to thesecond symbol, when the acknowledgement, information is positive, andapplies the first code to the second symbol, when the acknowledgementinformation does not exist.

In accordance with another aspect of the invention, a method is providedfor receiving information symbols in a communication system. The methodincludes receiving a first symbol and a second symbol; identifying aChannel Quality Indicator (CQI) based on the first symbol; andidentifying acknowledgement information based on the second symbol. Afirst code is applied to the second symbol, when the acknowledgementinformation is negative, a second code is applied to the second symbol,when the acknowledgement information is positive, and the first code isapplied to the second symbol, when the acknowledgement information doesnot exist.

In accordance with another aspect of the invention, apparatus isprovided for receiving information symbols in a communication system.The apparatus includes a receiver that receives a first symbol and asecond symbol; and a controller that identifies a Channel QualityIndicator (CQI) based on the first symbol, and that identifiesacknowledgement information based on the second symbol. A first code isapplied to the second symbol, when the acknowledgement information isnegative, a second code is applied to the second symbol, when theacknowledgement information is positive, and the first code is appliedto the second symbol, when the acknowledgement information does notexist.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of the presentinvention will be more apparent from the following detailed descriptiontaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagram illustrating an exemplary slot structure for anSC-FDMA communication system;

FIG. 2 is a diagram illustrative of an exemplary partitioning of a firstslot structure for the transmission of CQI bits;

FIG. 3 is a block diagram illustrative of a first exemplary SC-FDMAtransmitter for transmitting a CQI signal or a reference signal using aCAZAC-based sequence in the time domain;

FIG. 4 is a block diagram illustrative of a first exemplary SC-FDMAreceiver for receiving a CQI signal or a reference signal using aCAZAC-based sequence in the time domain;

FIG. 5 is a block diagram illustrative of a second exemplary SC-FDMAtransmitter for transmitting a CQI signal or a reference signal using aCAZAC-based sequence in the frequency domain;

FIG. 6 is a block diagram illustrative of a second exemplary SC-FDMAreceiver for receiving a CQI signal or a reference signal using aCAZAC-based sequence in the frequency domain;

FIG. 7 is a block diagram illustrating an exemplary construction oforthogonal CAZAC-based sequences through the application of differentcyclic shifts on a root CAZAC-based sequence;

FIG. 8 is a diagram illustrative of a prior art method for multiplexingCQI bits and ACK/NACK bits by puncturing some of the CQI bits andreplacing them with ACK/NACK bits;

FIG. 9 is a diagram illustrative of implicit multiplexing of ACK/NACKbits in a CQI transmission slot by applying an orthogonal cover to thesymbols in the slot that carry the reference signal, wherein theorthogonal cover depends on the value of the ACK/NACK bits; and

FIG. 10 is a diagram illustrative of implicit multiplexing of ACK/NACKbits in a CQI transmission slot by applying an orthogonal cover to thesymbols in the slots that carry the reference signal, wherein theorthogonal cover depends on the value of the ACK/NACK bits and the sameorthogonal cover is used when NACK is multiplexed and when no ACK/NACKbits exist.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Various embodiments of the present invention will now be described morefully hereinafter with reference to the accompanying drawings. Thepresent invention may, however, be embodied in many different forms andshould not be construed as limited to the embodiments set forth herein.Rather, these illustrative embodiments are provided so that thisdisclosure will be thorough and complete and will fully convey the scopeof the invention to those skilled in the art.

Additionally, although the present invention is described with referenceto a Single-Carrier Frequency Division Multiple Access (SC-FDMA)communication system, it also applies to all FDM systems in general andto Orthogonal FDMA (OFDMA), OFDM, FDMA, Discrete Fourier Transform(DFT)-spread OFDM, DFT-spread OFDMA, Single-Carrier OFDMA (SC-OFDMA),and SC OFDM in particular.

The embodiments of the present invention solve problems related to theneed for multiplexing the transmission of acknowledgement (ACK/NACK)signals and Channel Quality Indicator (CQI) signals transmitted by aUser Equipment (UE) in the absence of information data signals, forenabling reliable reception for both of these signals, for providingrobust system operation as a result of the multiplexing ACK/NACK and CQIsignals, and for facilitating the use of substantially the sametransmitter and receiver structures with minimal modifications, whenmultiplexing the previous two signals, with respect to the correspondingstructures for support of only CQI signaling.

As described above in the background, the CQI transmission from a UE ina Physical Uplink Control CHannel (PUCCH), which is typically periodicin nature, may occur in the same sub-frame as the ACK/NACK signaltransmission to support Hybrid Automatic Repeat reQuest (HARQ)(HARQ-ACK) in response to a prior data reception by the UE in thedownlink of the communication system. As the ACK/NACK signaltransmission usually cannot be postponed, it is beneficial to multiplexit with the CQI signal transmission. Otherwise, the CQI signaltransmission should be dropped, which may cause schedulinginefficiencies in the downlink of the communication system due to theabsence of relevant CQI.

The present invention considers embedding the ACK/NACK bits onto thereference signal (RS) transmitted together with the CQI signal in eachslot (in different SC-FDMA symbols). This is accomplished by having theUE apply orthogonal covering to the RS depending on the transmittedACK/NACK bits.

One exemplary embodiment for applying orthogonal covering to the RS inthe CQI slot structure depending on the existence and value of ACK/NACKbits is illustrated in FIG. 9. Compared to FIG. 2, in FIG. 9, the CQItransmission 920 in the slot 910 remains the same and the samemultiplexing 930 with a CAZAC-based sequence 940 applies. The RS 950 isalso constructed from a (un-modulated) CAZAC-based sequence. Thedifference originates from the multiplication of each of the two RS witheach element, W1 960 and W2 970, of a length−2 orthogonal cover.Different orthogonal covers correspond to positive (ACK) and negative(NACK) acknowledgement signals. Therefore, no explicit ACK/NACKsignaling is performed by the UE and the ACK/NACK information isimplicitly mapped into the RS.

As the covering applied to the RS in FIG. 9 is orthogonal (such aslength−2 Walsh/Hadamard codes), the Node B receiver can simply averagethe two RSs, after applying each of the possible de-covering operations,when it expects both CQI and ACK/NACK transmission. The result will beonly noise for the incorrect covers, while it will be the channelestimate for the correct one.

Subsequently, by performing separate decoding operations and selectingthe one maximizing a decision metric, as it is known in the art, theselection for the transmission of either CQI only, or CQI and ACK, orCQI and NACK can be made. Because the incorrect ones have only noise forthe corresponding channel estimate (no RS power), the likelihood ofselecting the correct hypothesis is not materially affected. IncorrectCQI decoding is still dominated by the hypothesis with the correctsetting regarding the ACK/NACK transmission.

Alternatively, the Node B may avoid having to perform separate decodingoperations and rely on the accumulated energy after averaging the twoRSs, after the de-covering operation. The magnitude of the resultingcomplex signal after averaging is used to obtain its energy. The correcthypothesis results in larger signal energy than the incorrect ones thatcontain only noise. After a decision for the RS orthogonal cover that isused at the transmitter is made, based on the largest resulting energyamong the possible orthogonal covers as described above, the receiverapplies that orthogonal cover to the RS in order to obtain a channelestimate used for coherent demodulation of the CQI signal.

In an exemplary embodiment of the present invention, based on theaccumulated energy, which is obtained by averaging the two RSs in eachslot for each of the possible orthogonal covers, a decision on theACK/NACK value can be made. The accuracy of this decision is typicallymuch better than the usual reception reliability requirements for theCQI. Therefore, the CQI performance remains unaffected by the ACK/NACKmultiplexing and the desired accuracy for the ACK/NACK decision is alsoachieved.

In practice, the multiplication with W1 and W2 in FIG. 9 is notnecessary. Either the resulting signal, after the IFFT, is transmittedas the RS (multiplication by 1) or it has its sign inverted(multiplication with −1). For high UE speeds, where RS averaging (RSaddition or RS subtraction) is not as reliable due to the higher channelvariation, the performance of the above decoding method is somewhataffected as for the incorrect hypotheses the result of RS averaging willstill be noise but with a higher variance compared to the case of low UEspeeds where the channel variations are smaller and the RS value,excluding noise, remains largely unchanged in the two correspondingsymbols in each slot.

Complex scaling coefficients for the RS can also be used to increase thenumber of possible combinations of CQI and ACK/NACK bits that can bedetected. For example, this can be applicable for the case of twoACK/NACK bits and two RS symbols per slot and effectively QPSKmodulation may apply on the RS depending on the value of the twoACK/NACK bits.

In addition to the general principle of multiplexing ACK/NACKinformation into the CQI transmission structure by applying anorthogonal cover on each of the two RSs in a slot of the exemplaryembodiment, the present invention further considers the overall systemrobustness to ACK/NACK errors.

In particular, the present invention considers the error case where theUE has missed a downlink scheduling assignment and therefore it is notaware that it needs to multiplex ACK/NACK in its CQI transmission, whenthe two happen to coincide in the same transmission time interval, whilethe serving Node B expects that ACK/NACK is multiplexed. The absence ofACK/NACK transmission from a UE, due to missing the correspondingdownlink scheduling assignment, is herein referred to as DiscontinuousTransmission (DTX) (of ACK/NACK).

The main objective is for the Node B to avoid interpreting DTX as an ACKbecause this will cause erroneous operation at the physical layer as theNode B will assume that the UE received the data packet and will notre-transmit it. Instead, additional packet transmissions may followbefore this error is realized by the higher layers of the communicationsystem, thereby wasting radio resources and increasing latency for thecommunication session.

DTX interpretation as a NACK does not cause any serious operationperformance issues because the Node B may always choose to interpret DTXas NACK and retransmit the packet, possibly with a different redundancyversion of the HARQ process, as it is known in the art, or interpret theNACK as the DTX and simply retransmit the packet with the sameredundancy version. Assuming turbo coding is used, the former approachmay be used for low or medium coding rates of the data packet, wheresystematic bits are present in the packet retransmission, while thelatter approach may be used for high coding rates to ensure the presenceof systematic bits in retransmissions. In either case, the performancedegradation of the packet reception, if any, is limited and does nothave a meaningful impact on the communication session or the systemthroughput.

The positive tradeoff is that the Node B needs to only perform a 2-statedetection (ACK or NACK) instead of a 3-state one (ACK, NACK, or DTX).This aspect of the present invention enhances the ACK/NACK detectionreliability and improves the system operation and throughput.

The present invention incorporates the above observations into furtherrefining the selection of the orthogonal cover applied to the associatedRS in a slot of CQI transmission in the PUCCH. The rule applied for thisselection is such that the DTX and NACK states are collapsed onto thesame state, which the Node B may interpret either as a DTX or as a NACK.

An exemplary embodiment considers the case of 1-bit ACK/NACKtransmission and is illustrated in FIG. 10. In FIG. 10, the onlydifference relative to FIG. 9 is the specific orthogonal cover appliedto the ACK and NACK.

Referring to FIG. 10, as DTX and NACK are collapsed onto the same state1080, they correspond to the same code. As the exemplary embodimentassumes that no orthogonal cover applies to the RS when only CQI(without ACK/NACK multiplexing) is transmitted, the orthogonal coverused to indicate DTX and NACK is {1, 1}. Conversely, ACK is embedded byapplying the {1, −1} orthogonal cover 1090 to the RS symbols in the CQItransmission slot.

When ACK/NACK information is expected to be included with the CQItransmission in the PUCCH, the Node B receiver can simply remove thebinary covering for each of the two hypotheses in FIG. 10 and obtain twocorresponding channel estimates. No additional operation is necessaryfor the hypothesis corresponding to the orthogonal cover of {1, 1} (DTXor NACK), while for the hypothesis corresponding to the orthogonal coverof {1, −1} (ACK), the signal received during the SC-FDMA symbolcorresponding to the second RS is reversed (multiplication with “−1”).Therefore, the process for removing the orthogonal cover at the Node Breceiver is the same as the one for applying it at the UE transmitter(FIG. 10).

While the present invention has been shown and described with referenceto certain exemplary embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the presentinvention as defined by the appended claims.

What is claimed is:
 1. A method for transmitting information symbols ina single-carrier frequency division multiple access communicationsystem, the method comprising: determining a Channel Quality Indicator(CQI) and acknowledgement information, in response to data reception;generating a first symbol based on the CQI and a second symbol based onthe acknowledgement information; and transmitting the first symbol andthe second symbol, wherein a first code is applied to the second symbol,when the acknowledgement information is negative, a second code isapplied to the second symbol, when the acknowledgement information ispositive, and the first code is applied to the second symbol, when theacknowledgement information does not exist.
 2. The method of claim 1,wherein the first code is {1 }.
 3. The method of claim 2, wherein thesecond code is {−1}.
 4. The method of claim 1, wherein the second symbolis based on the acknowledgement information and a reference signal. 5.An apparatus for transmitting information symbols in a single-carrierfrequency division multiple access communication system, the apparatuscomprising: a controller that determines a Channel Quality Indicator(CQI) and acknowledgement information, in response to data reception,generates a first symbol based on the CQI, and generates a second symbolbased on the acknowledgement information; and a transmitter thattransmits the first symbol and the second symbol, wherein the controllerapplies a first code to the second symbol, when the acknowledgementinformation is negative, applies a second code to the second symbol,when the acknowledgement information is positive, and applies the firstcode to the second symbol, when the acknowledgement information does notexist.
 6. The apparatus of claim 5, wherein the first code is {1}. 7.The apparatus of claim 6, wherein the second code is {−1}.
 8. Theapparatus of claim 5, wherein the controller generates the second symbolbased on the acknowledgement information and a reference signal.
 9. Amethod for receiving information symbols in a single-carrier frequencydivision multiple access communication system, the method comprising:receiving a first symbol and a second symbol; identifying a ChannelQuality Indicator (CQI) based on the first symbol; and identifyingacknowledgement information based on the second symbol, wherein a firstcode is applied to the second symbol, when the acknowledgementinformation is negative, a second code is applied to the second symbol,when the acknowledgement information is positive, and the first code isapplied to the second symbol, when the acknowledgement information doesnot exist.
 10. The method of claim 9, wherein the first code is {1}. 11.The method of claim 10, wherein the second code is {−1}.
 12. The methodof claim 9, further comprising identifying a reference signal from thesecond symbol.
 13. An apparatus for receiving information symbols in asingle-carrier frequency division multiple access communication system,the apparatus comprising: a receiver that receives a first symbol and asecond symbol; and a controller that identifies a Channel QualityIndicator (CQI) based on the first symbol, and that identifiesacknowledgement information based on the second symbol, wherein a firstcode is applied to the second symbol, when the acknowledgementinformation is negative, a second code is applied to the second symbol,when the acknowledgement information is positive, and the first code isapplied to the second symbol, when the acknowledgement information doesnot exist.
 14. The apparatus of claim 13, wherein the first code is {1}.15. The apparatus of claim 14, wherein the second code is {−1}.
 16. Theapparatus of claim 13, wherein the controller identifies a referencesignal from the second symbol.